Of conventional capacitive sensors, for example, some are single end output type and the other of the capacitive sensors are differential output type. As for C-V converter circuits that convert sensor output signals into voltages, some are configured to use an amplifier circuit with a single end configuration and the other are configured to use an amplifier circuit with a differential configuration. (Refer to JP-2008-216135A, for example.) For this reason, the specifications of an amplifier circuit forming a C-V converter circuit therein are determined in correspondence to the output method (form) of a sensor used. Therefore, when the specifications of a sensor used are changed, it is necessary to change the specifications (circuit configuration) of an amplifier circuit forming the C-V converter according to such changes.
Many A/D converters incorporated into a microcomputer are of single end input type and many discrete A/D converters are of differential input type. For this reason, when an analog signal outputted from a signal processor circuit is converted to a digital signal, it is necessary to take the output method (single end output or differential output) of an amplifier circuit forming the output stage of the signal processor circuit according to the input method of the A/D converter used.
For the purpose of shortening an integrated circuit (IC) development period, reducing total costs, and the like, IC modules in which the functions of an analog circuit as well as a digital circuit are programmable are under development. In such an IC module, an amplifier circuit (amplifier) whose signal output form or method can be dynamically switched may be required.
In both cases where a sensor is of single end output type and where it is of differential output type, a C-V converter circuit using an amplifier circuit with a differential configuration could be used in common. This makes it unnecessary to change the specifications of the amplifier circuit according to the output method of the sensor. In this case, however, an input common mode feedback circuit is required to keep the common mode level of input signals supplied to each input terminal of the amplifier circuit at a predetermined level. For this reason, when a sensor of single end output type is used, an input common mode feedback circuit that is otherwise unnecessary is necessary in a C-V converter circuit using an ordinary amplifier circuit with a single end configuration. This accordingly increases the circuit area.